Supersonic shock wave tuyere

ABSTRACT

A supersonic shockwave tuyere for injecting a mixture of fuel into a shaft furnace. The tuyere has a convergent and a divergent portion and a sonic throat at the junction of the two portions. The convergent portion, the sonic throat and the first part of the divergent portion are formed in a first member which is releasably connected to a second member which forms a second part of the divergent portion, whereby upon change in the rate of the supply medium for support of the combustion, the first part may be exchanged against another part to modify the sonic throat as a function of such change.

United States Patent [1 1 Borgnat et a1.

[ Nov. 4, 1975 SUPERSONIC SHOCK WAVE TUYERE [22] Filed: Jan. 9, 1974[21] Appl. No.: 431,964

[30] Foreign Application Priority Data .Ian. 18, 1973 France 73.01692[52] US. Cl. 266/41 [51] Int. Cl. C21B 7/16 [58] Field of Search110/1825; 122/66;

[56] References Cited UNITED STATES PATENTS 3,015,481 1/1962Clingensmith 266/41 3,558,119 1/1971 Demalander 1. 266/41 3,793,0021/1974 Borgnat et al. 75/60 FOREIGN PATENTS OR APPLICATIONS 26,03711/1903 United Kingdom 266/41 Primary Examiner-Gerald A. Dost Attorney,Agent, or FirmMichae1 S. Striker 57 7 ABSTRACT A supersonic shockwavetuyere for injecting a mixture of fuel into a shaft furnace. The tuyerehas a convergent and a divergent portion and a sonic throat at thejunction of the two portions. The convergent portion, the sonic throatand the first part of the divergent portion are formed in a first memberwhich is releasably connected to a second member which forms a secondpart of the divergent portion, whereby upon change in the rate of thesupply medium for support of the combustion, the first part may beexchanged against another part to modify the sonic throat as a functionof such change.

9 Claims, 4 Drawing Figures U.S. Patent Nov. 4, 1975 Sheet 1 of23,917,243

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US. Patent Nov. 4, 1975 Sheet 2 of2 3,917,243

FIG.3

SUPERSONIC SHOCK WAVE TUYERE BACKGROUND OF THE INVENTION The presentinvention relates to a shock wave tuyere of the type used in shaftfurnaces to effect mixing of a fuel and a combustion-support medium, andthe combustion of this mixture.

It has been proposed that part of the solid fuel used in shaft furnaces,in particular blast furnaces, bereplaced by an auxiliary hydrocarbonfuel, for instance in liquid form, this fuel being injected into blastpipes opening into the shaft furnaces. Since the cost of solid fuel, ingeneral coke, is relatively high, the effect of injecting an auxiliaryfuel on the cost price of the product prepared in the shaft furnacedepends on the rate of injection of auxiliary fuel. Attempts havetherefore been made to reach injection rates as high as possible, whileremaining compatible with satisfactory operation of the shaft furnace,especially from the aspect of the outflow of the charges treated in thesaid furnace. However, experience has shown that the auxiliary fuelinjected burns increasingly incompletely as the injection rate rises,this incomplete combustion being accompanied by the formation of soot.This phenomenon necessitates keeping the auxiliary fuel injection rateat relatively low values. 7

The injection rate of a fuel may be substantially raised by increasingthe degree of dispersion of the fuel in the gaseouscombustion-supporting medium, and this enables the combustion conditionsto be improved. One technique perfected by the applicants for thispurpose consists in creating, in a tuyere of the Laval type forintroducing fuel into a shaft furnace, a supersonic outflow inconditions such that the transition from the supersonic discharge rateto the subsonic discharge rate takes place in the divergent portion ofthe tuyere, that is to say that a shock wave is formed in said divergentportion, and in injecting a fuel into said tuyere upstream of said shockwave. Tests carried out with tuyeres of this type have shown theeffectiveness of the action of dispersing the fuel in thecombustion-support medium as it passes into the shock wave zone, thistechnique consequently permitting high fuel injection rates to be usedwithout forming soot.

For a given pressure of the combustion-support medium at the inlet endof a tuyere of the type aforesaid it is known to calculate thegeometrical characteristics of the tuyere to achieve the formation ofthe shock wave in the divergent portion of the tuyere. There are limitswithin which this pressure may vary, while maintaining the shock wave inthe divergent portion of the tuyere and downstream of the fuel injectionzone. Too large a pressure drop may however involve noncompliance withthese conditions, and too large a pressure rise may lead to generating asupersonic outflow rate at the outlet from the divergent length of thetuyere. The extent of these limits between which the'pressure may varydepends on the value of the pressure at the tuyere inlet, but isrelatively restricted for the values envisaged in the context ofintroducing a combustion-support medium into a shaft furnace, forexample hot air into a blast furnace. This is not in fact a seriousdisadvantage, since blast furnaces are increasingly designed to operateabout a relatively constant reference pressure, corresponding to the airflow for the maximum production considered. It is thus permissible todesign tuyeres in such manner as to allow the maximum injection rate ofauxiliary fuel commensurate with a tuyere geometry adapted to thereference pressure.

However, it may be found necessary to operate the shaft furnace at arate other than that corresponding to the maximum production. In orderto retain the advantages of auxiliary fuel injection during thecorresponding periods, one must either replace all the injection tuyeresby a set of tuyeres of a geometry adapted in shape and size to the newoperating rate, this constituting an extremely tedious operation whichmust in practice be excluded, or universal tuyeres must be designed withvariable geometry, of relatively complex construction and doubtfulreliability.

SUMMARY OF THE INVENTION The object of the invention is to obviate ormitigate the aforesaid disadvantages, and more particularly to permitadaptations of the geometry of a tuyere for injecting an auxiliary fuelinto a shaft furnace as a function of changes in the operating rate ofsaid furnace, in order to permit maintenance of a maximum auxiliary fuelinjection rate independently of changes in the rate of operation.

To this end, the subject of the invention is a supersonic shock wavetuyere for injecting a mixture of fuel and combustion-support mediuminto a shaft furnace. The tuyere has a convergent portion and adivergent portion with a sonic throat formed at the junction of theportion, said tuyere comprising a first member forming the convergentportion, the sonic throat and a first part of the divergent portion, asecond fixed member forming a second part of the divergent portion, andmeans for removably connecting the first to the second member so thatthe first and second parts of the divergent portion are joined to formextensions of each other, whereby, upon change in the rate of supply ofmedium for support of combustion, the first member may be exchangedagainst another member to modify the sonic throat as a function of suchchange.

According to a preferred feature, the first member is equipped withmeans for injecting fuel into the tuyere, said tuyere being connected toa source of gaseous combustion-support medium.

According to afurther feature, the source of combustion-support mediumis constituted by the circulation of hot blast from a blast furnace.

According to a further feature, the divergent portion and the convergentportion are constituted by co-axial surfaces of revolution, the firstand the second part of the divergent'portions have the same cone angleand the sonic throat is constituted by the intersection of the surfacesof revolutions constituting the convergent and divergent portions in aplane normal to the common axis of these surfaces.

By virtue of its construction by two independent members, the tuyereaccording to the invention enables its geometric features to be modifiedwith a view to adapting said features to a change in the rate of supplyto the tuyere of combustion-support medium, so as to maintain specificflow conditions in the tuyere.

It will be understood that a change in the operating rate of a shaftfurnace fitted with shock wave tuyeres for injecting fuel into a flow ofgaseous combustionsupport medium conveyed at supersonic speed, whichchange is manifested as a change in the flow rate and pressure of thecombustion-support medium at the inlet of the tuyere, will involve achange in the flow properties of the combustion-support medium in saidtuyere. In order to maintain in the divergent portion of the tuyere ashock wave indispensible for satisfactory dispersion of the fuel, thesonic throat stage is correlatively modified by replacing theinterchangeable member, which forms a species of a head of'the tuyere,by a similar member adapted to the new conditions prevailing at the headend, of the tuyere, the similar member having a sonic throat ofdifferent working section determined as a function of the new conditionsof pressure and flow rate. This replacement can be effected very rapidlywithout removing the part of the tuyere integrated with the shaftfurnace, and affects a readily accessible part of the tuyere.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the accompanying drawingshows a longitudinal section through one embodiment of a tuyereaccording to the invention for supplying auxiliary fuel into a blastfurnace;

FIG. 2 illustrates, in cross-section a detail of FIG. 1; and

FIGS. 3 and 4 illustrate, likewise in cross-section, differentlydimensioned elements which may be placed in the embodiment of FIG. 1,instead of the corresponding element shown therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawing shows ablast-furnace tuyere l of the shock wave type, this tuyere being diposedas an extension of a pipe 2 connected to the blast pipe of a blastfumace. The internal surface of the tuyere 1 is symmetrical about thelongitudinal axis of the tuyere and includes a convergent portion 3 anda divergent portion 4. Where the portions 3 and 4 come together, thereis formed a constriction or throttling portion 5, hereinafter called thesonic throat. The tuyere is fixed to an annular, preferably water cooledsupport 6 integral with the blast-furnace wall, and issues into theinterior of the furnace near the upper part of the hearth.

In accordance with the invention, the tuyere is constituted by theassociation of two mutually complementary parts assembled together so asto constitute the internal profile of the tuyere, namely a firstinterchangeable member 7 forming a tuyere head and including theconvergent portion '3, the sonic throat and a first part 4a of thedivergent port-ion, and a second substantially fixed member 8 formingthe tuyere nose and including a second part 4b of the divergent portionissuing directly into the blast furnace interior, the second memberbeing fixedly connected to the support 6. The tuye're nose comprises ahollow copper body 9 joined by brazing to a suppor plate 10 having anexternal frustoconical bearing surface 11 cooperating with acorresponding internal bearing surface formed in the support 6. Aninternal jacket or casing 12 is arranged in the body 9 and is incommunication via a conduit 13 passing through the support plate with asource of cooling liquid; the jacket 12 is also in communication withthe interior of the body 9 through apertures 14 arranged at the end ofthe jacket, draining offof the cooling liquid taking place through holes(not shown)-provided in the support plate. The member 7 has an externalcentering bearing surface 15 and an abutment surface 16 which cooperaterespectively with an intermal bearing surface 17 of the support plate 10and with the external surface of the support plate in such manner thatthe member 7 and the nose of the tuyere can be contiguously disposed,with the convergent part 4b of the nose forming an extension of theconvergent part 4a of the member 7. The first and second member of thetuyere may be joined together by screws 18 located at intervals. Anannular groove 19 is provided in the abutment surface 16 of the member 7so as to form a chamber communicating both with theexterior of thetuyere via conduits 20 for admission-of auxiliary fuel and with theinterior of the tuyere near to the sonic throat 5 through injectionconduits 21 directed towards the axis of the sonic throat. A fluid-tightpacking 22 is located in a groove 23 provided in the external surface ofthe support plate 10, this packing being compressed by-an annularprojection 24 when the member 7 is mounted on the support plate. Thepipe 2 is applied against a shoulder 25 on the member 7 by a tighteningdevice 26 which enables rapid disconnection of the pipe 2. 4

As far as the manner of operation of the shock wave type tuyeres isconcerned, it should beborne in mind that the internal profile of thetuyere, and in particular the surface area of the sonic throat,-isdesigned for given values of the feed pressure, also known as thegenerating pressure, and of the ejection pressure, so that thecombustion-supporting medium getting into the tuyere, in this case thehot blast, reaches the supersonic speed range at the tuyere throat, andthat the transition to the subsonic speed range takes place in the 1divergent portion with correlative formation of a shock wave in saiddivergent portion. An auxiliary fuel such as a liquid hydrocarbon isintroduced under pressure into the chamber 19 and is injected into thetuyere via the conduits 21. The auxiliary fuel entrained by the currentof combustion-support medium mixes intimately therewith on passagethrough the shock wave formation zone, the mixture spontaneously ignitesdownstream of said zone under the effect of the ambient temperature andcombustion will take place without formation of soot even at relativelyhigh auxiliary fuel injection rates as compared with the rates appliedin the art taken into consideration of injecting auxiliary fuel intoblast furnaces. The tuyere profile is so fashioned that the fluctuationsin pressure may reach 20% of the feed pressure corresponding to thedesired rate of operation without causing upsets in the normal operationof thetuyere.

When it proves to be desirable to establish a different operating ratein the blast furnace, for instance,

because the production of pig iron should be altered, the blast rate mayvary in such manner that the tuyere profile no longer permits supersonicflow to be induced in the tuyere. The rate of injection of auxiliaryfuel which can then be contemplated without forming soot. may then bereduced by more than half, which results in making pig iron at higherunit cost price. .The tuyere according to the invention enables thetuyere geometry to be rapidly adjusted to the new operation conditions.

It is known that the mass flow rate of a supersonic tuyere isproportional to the pressure prevailing atthe tuyere inlet and to thesurface area of the sonic throat.

The profile of the tuyere is determined by rules', well;

known to those skilled in the art for given values of feed rate andpressure, so that supersonic flow may be established in the tuyere withtransition to the subsonic speed range in the divergent portion. Theflow characteristics in the tuyere may be maintained when the flow rateis established at a value different from the preceding value, providedthat substantially the same pressure prevails at the tuyere inlet, aresult which may be obtained by modifying the extent of the sonic throatsurface area. In order to do this, the pipe 2 is first removed, theblast delivery appropriate to the tuyere contemplated having beentemporarily interrupted, then the first tuyere member 7 is removed andis replaced by another first member 7 or 7" so formed that the surfacearea of the sonic throat 5' or 5" differs from the surface area of thesonic throat 5 of the member 7; the ratio of the surface areas beingsubbstantially proportional to the ratio of flow rates for a given blasttemperature. There is one feature common to the different first memberstuyere in that the sonic throat thereof is constituted by the sectionthrough a plane perpendicular to the tuyere axis of a frusto-conicalsurface of revolution which has the same cone angle as the second part4b of the divergent portion where the first part 4a of the divergentportion comes together with the second part 4b of said divergentportion. This surface of revolution is represented in broken lines andis denoted by the reference S in the drawing. The term frusto-conicalsurface is to be construed as indicating surfaces derived from bothrectilinear and curvilinear generating lines, this latter casecorresponding to tuyeres the divergent portion of which is of flaredtubular shape. Moreover, the divergent portion may have this shape onlyin its second part 4b. It should be understood that the axial length ofthe divergent part 4a of the tuyere may be reduced until the surfacearea of the sonic throat corresponds to the surface area delimited bythe circumference where the first and the second part of the tuyere cometogether.

The tuyere in accordance with the invention constitutes an injectiondevice for gases and in particular for reducing gas mixtures which mayfind application in any plant involving the introduction of such gasmixtures. The tuyere finds particular application in shaft furnaces withthe object of effecting the supply of a fuel and the combustion of thefuel in optimum conditions, while enabling these conditions to bemaintained for different rates of feed of the medium supplied to thetuyere to support combustion. The fuel used may be a gaseous or liquidhydrocarbon product and may be particles of solid fuel in suspension ineither of these media, as well as carrying any material which it isdesired to introduce into the shaft furnace in a form compatible withthe functioning of the injection device. The formation of the tuyere intwo parts, one of which includes the fuel injection device, also enablesthe properties of this injection device to be selected as a function ofthe nature of the fuel injected. The invention is particularlyapplicable for the injection of an auxiliary fuel such as fuel oil bythe tyeres of a blast furnace with a view to replacing part of the cokeused by this auxiliary fuel.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types oftuyeres differing from the types described above.

While the invention has been illustrated and described as embodied in atuyere for the injection of an auxiliary fuel, such as fuel oil, into ablast furnace, it is not intended to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting in any way from the spirit of H the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended 1. A supersonic shock wave tuyere forinjecting a mixture of fuel and a combustion-supporting medium into ashaft furnace, said tuyere having an unobstructed passage including aconvergent portion and a divergent portion with a sonic throat at thejunction of said portions, said tuyere comprising a first member formingsaid convergent portion, said sonic throat and a first part of saiddivergent portion; a fixed. hollow internally cooled second memberforming a second part of said divergent portion; and means for removablyconnecting said first member to said second member so that said firstand second parts of said divergent portion are joined to form extensionsof each other whereby upon change of the rate of the supply medium forsupport of combustion, said first member may be exchanged for adifferent first member having a different throat area and adapted to beplaced against the original second member to modify the sonic throat asa function of said change.

2. A tuyere as defined in claim 1, and including means incorporated insaid first member for injecting fuel into the tuyere, and meansconnected to said first member for passing a gaseouscombustion-supporting medium into the tuyere.

3. A tuyere as defined in claim 2, wherein said combustion-supportingmedium is taken from a supply circuit of hot blast to a blast furnace.

4. A tuyere as defined in claim 2, wherein said divergent and convergentportions are constituted by coaxial surfaces of revolution, wherein saidfirst and said second part of said divergent portion have the same coneangle, and wherein said sonic throat is constituted by the intersectionof said surfaces constituting said divergent and convergent portions ina plane nonnal to the common axis of said portions.

5. A tuyere as defined in claim 2, wherein said means for injecting fuelinto said tuyere comprises an annular chamber formed in said firstmember, passage means for feeding fuel into said annular chamber, and aplurality of passages communicating at opposite ends with said annularchamber and with the interior of said first part of said divergentportion downstream of said sonic throat.

6. A tuyere as defined in claim 2, wherein said second member comprisesa support plate provided with a central opening defined by afrustoconical surface and a hollow body coaxially joined to said supportplate and port plate has an external frustoconical bearing surface, andincluding an annular support member adapted to be mounted in an openingof the shaft furnace, said support member having an internalfrustoconical surface tightly engaged by said external frustoconicalsurface of said support plate.

9. A tuyere as defined in claim 6, wherein said connecting meansremovably connect said first member to said support plate.

1. A supersonic shock wave tuyere for injecting a mixture of fuel and acombustion-supporting medium into a shaft furnace, said tuyere having anunobstructed passage including a convergent portion and a divergentportion with a sonic throat at the junction of said portions, saidtuyere comprising a first member forming said convergent portioN, saidsonic throat and a first part of said divergent portion; a fixed, hollowinternally cooled second member forming a second part of said divergentportion; and means for removably connecting said first member to saidsecond member so that said first and second parts of said divergentportion are joined to form extensions of each other whereby upon changeof the rate of the supply medium for support of combustion, said firstmember may be exchanged for a different first member having a differentthroat area and adapted to be placed against the original second memberto modify the sonic throat as a function of said change.
 2. A tuyere asdefined in claim 1, and including means incorporated in said firstmember for injecting fuel into the tuyere, and means connected to saidfirst member for passing a gaseous combustion-supporting medium into thetuyere.
 3. A tuyere as defined in claim 2, wherein saidcombustion-supporting medium is taken from a supply circuit of hot blastto a blast furnace.
 4. A tuyere as defined in claim 2, wherein saiddivergent and convergent portions are constituted by coaxial surfaces ofrevolution, wherein said first and said second part of said divergentportion have the same cone angle, and wherein said sonic throat isconstituted by the intersection of said surfaces constituting saiddivergent and convergent portions in a plane normal to the common axisof said portions.
 5. A tuyere as defined in claim 2, wherein said meansfor injecting fuel into said tuyere comprises an annular chamber formedin said first member, passage means for feeding fuel into said annularchamber, and a plurality of passages communicating at opposite ends withsaid annular chamber and with the interior of said first part of saiddivergent portion downstream of said sonic throat.
 6. A tuyere asdefined in claim 2, wherein said second member comprises a support plateprovided with a central opening defined by a frustoconical surface and ahollow body coaxially joined to said support plate and defining afrustoconical passage of the same cone angle as said opening in saidsupport plate.
 7. A tuyere as defined in claim 6, wherein said hollowbody is formed from a material having high thermal conductivity, andincluding a jacket arranged in said hollow body spaced from the innersurface thereof, and means for circulating a cooling fluid through saidjacket and through the space between the latter and the inner surface ofsaid hollow body.
 8. A tuyere as defined in claim 6, wherein saidsupport plate has an external frustoconical bearing surface, andincluding an annular support member adapted to be mounted in an openingof the shaft furnace, said support member having an internalfrustoconical surface tightly engaged by said external frustoconicalsurface of said support plate.
 9. A tuyere as defined in claim 6,wherein said connecting means removably connect said first member tosaid support plate.